Tire molding is typically carried out by setting an uncured (green) tire in a mold and then inserting a butyl rubber sac-like member called the tire bladder on the inside of the green tire, pressing the green tire against the mold from the inside by inflating the tire bladder with high-temperature, high-pressure steam, and heating in this state to cure the tire. To allow the tire bladder to be stripped from the tire after molding, a release agent is applied to the inner wall of the green tire and the surface of the tire bladder. Liquid silicone-containing compositions and curable silicone-containing compositions are used as the release agent that is applied to the surface of the tire bladder.
Examples of liquid silicone-containing compositions include compositions containing a polydimethylsiloxane having a viscosity of 40,000 to 120,000 mm2/s and bentonite clay (JP-A S57-119992: Patent Document 1), compositions containing a polydimethylsiloxane having a viscosity of 15×106 to 25×108 mm2/s, a polydimethylsiloxane having a viscosity of 40,000 to 120,000 mm2/s and bentonite clay (JP-A S57-111393: Patent Document 2), compositions containing a polyorganosiloxane having an average degree of polymerization of 2,500 to 6,000 and a polyorganosiloxane having an average degree of polymerization of 800 to 1,600 (JP-A S63-147610: Patent Document 3), and compositions containing a silicone oil a viscosity of having at least 100 mPa·s and a silicone rubber powder (JP-A 2000-158454: Patent Document 3).
Applying a release agent after the tire bladder has been mounted on the tire molding machine is difficult, and so it is desired that the release agent, when simply applied prior to use of the bladder, be capable of repetitive release. Although it is also possible to remove the tire bladder from the molding machine and again apply the release agent to it, this is an operation that takes considerable time and effort. With the above liquid silicone-containing compositions, the liquid silicone migrates to the tire side when the tire separates from the bladder, resulting in a loss of silicone from the bladder surface and thus poor repetitive releasability.
Curable silicone-containing compositions have therefore been described. Examples include compositions containing a silicone which forms a rubber under the application of heat (JP-A S59-106948: Patent Document 5), organopolysiloxane latex compositions obtained by emulsion polymerizing a cyclic diorganopolysiloxane or a diorganopolysiloxane capped with silanol at both ends with a functional group-bonded organotrialkoxysilane or a functional group-bonded organodialkoxysilane (JP-A S60-179211: Patent Document 6), compositions containing a diorganopolysiloxane having hydroxyl groups at both ends, an aminoalkyl group-containing hydrolyzable silane and an amino-modified organopolysiloxane (JP-A H06-134769: Patent Document 7), compositions containing a diorganopolysiloxane having hydroxyl groups at both ends, an aminoalkyl group-containing hydrolyzable silane, and a silicone oil having organic groups selected from aryl groups, aralkyl groups and polyether residues (JP-A H08-323773: Patent Document 8), compositions containing a hydroxyl- or alkoxy-terminated diorganopolysiloxane, a siloxane having an aminoalkyl group and a siloxane having an epoxy group (JP-A H11-198150: Patent Document 9), compositions containing a linear organopolysiloxane having hydroxyl groups, a polyorganosiloxane resin, and a crosslinking agent having a functional group capable of reacting with the polyorganosiloxane resin (JP-A 2005-527671: Patent Document 10), compositions containing a linear organopolysiloxane having hydroxyl or alkoxyl functional groups at both ends and either a hydroxylated or alkoxylated organopolysiloxane resin or a crosslinking agent having a hydroxyl or alkoxyl functional group (JP-A 2008-536967: Patent Document 11), and compositions containing a non-reactive linear organopolysiloxane, a reactive linear organopolysiloxane having hydroxyl groups, a silicone-compatible crosslinking agent and a triol silane having an aminoalkyl group (JP-A 2010-505970: Patent Document 12).
A curable silicone, after being applied to the surface of a tire bladder, forms a film having elasticity. This film must have an extensibility that enables it to follow stretching of the tire bladder when the bladder is inflated and must also be strong enough to not break or abrade upon rubbing against the tire when the bladder is stripped from the tire. Moreover, the film must strongly adhere to the bladder rubber when the bladder is in an inflated state, even at the curing temperature. Because fully satisfying these properties has been difficult, the repetitive release performance has been inadequate. Achieving strong adherence to the bladder rubber has been especially difficult. Efforts hitherto made to improve adherence to the bladder rubber include one method in which the bladder is first coated with a primer treatment agent and is subsequently coated with a rubber-forming silicone (JP-A S61-215015: Patent Document 13). In another such method, a room temperature-curable silicone rubber layer having adhesion to the bladder rubber is formed as an inner layer and a condensation-type silicone resin layer is formed as an outer layer (JP-A H06-339927: Patent Document 14). However, adherence remains inadequate.
Organohydrogenpolysiloxane-containing compositions have thus been disclosed. Examples include compositions containing an organohydrogenpolysiloxane, a hydroxyl group-containing organopolysiloxane rubber and a lubricant (JP-A S62-3908: Patent Document 15), compositions containing a compound having an Si—H group, an organopolysiloxane having a viscosity of from 3,000 to 5,000,000 mm2/s, and silica (JP-A S62-275711: Patent Document 16), and compositions containing an organohydrogenpolysiloxane and a diorganopolysiloxane end-capped with a trialkylsilyl group and having a viscosity of 6×106 to 1×1010 mPa·s (JP-A H11-114970: Patent Document 17). These have better repetitive release performances than the earlier-described compositions, presumably on account of the good adherence of the organohydrogenpolysiloxane to the bladder rubber. Organohydrogenpolysiloxanes are polymerizable, but the compositions do not necessarily cure to completion and organopolysiloxanes having a high degree of polymerization are thought to impart flexibility. However, because compositions containing these organohydrogenpolysiloxanes generate hydrogen gas when heated after being applied, there is a danger of the hydrogen gas igniting and causing an explosion or fire. Also, when such a composition is prepared as an emulsion, hydrogen evolution may arise even during storage. In addition, there exists a desire for further improvement in the repetitive release performance.
Compositions that include a liquid silicone having functional groups with a good adherence to bladder rubber have also been disclosed. Examples include compositions which include an aminoalkyl group-containing organopolysiloxane (JP-A S60-229719: Patent Document 18), compositions which include an organopolysiloxane containing hydrocarbon groups of 5 or more carbon atoms that have a C═C double bond (JP-A S61-100417: Patent Document 19), and siloxane compounds having a (meth)acryloyl group (JP-A 2010-241915: Patent Document 20).